Diarrhea

Published on 26/03/2015 by admin

Filed under Critical Care Medicine

Last modified 26/03/2015

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25 Diarrhea

Diarrhea is one of the most common abnormal manifestations of gastrointestinal (GI) dysfunction in the intensive care unit (ICU); the reported incidence is between 2% and 63%.1 Diarrhea is best defined as bowel movements that, owing to increased frequency, abnormal consistency, or increased volume, cause discomfort to the patient or the caregiver. This definition demonstrates the subjectivity in diagnosing diarrhea, a fact that complicates interpretation of the literature and limits applicability of guidelines. The impact of diarrhea on patient care in the ICU, including its cost in morbidity and mortality, is unknown. However, it is undeniable that diarrhea remains a persistent problem in many ICUs.

image Pathophysiology

Bowel movements with normal physiologic volume, consistency, and frequency are the result of a GI tract that integrates motility, secretion, and absorption of fluids and adapts to the quality of the food bolus given. The result is a fecal bolus that is produced once or twice every 24 hours and has consistency and fluidity within the boundaries of normal.

Diarrhea results when there is a disorder of GI physiology or when GI tract function is incapable of handling the food bolus. There are several classifications of diarrhea, suggesting that no classification is ideal at helping the clinician plan for patient care. Perhaps the most useful approach is to classify diarrhea according to alterations of physiologic events:

1 Increased fluid secretion that overwhelms absorption. On average, up to 9 liters of fluid is secreted into the GI lumen in addition to the normal oral intake. Less than 1% of that fluid is contained in stool, owing to the amazingly large absorptive capacity of the small and large bowel. Within the intestinal mucosa, passive and active transport of sodium determines the amount of water that is absorbed. Stimulation of the active secretion of fluids into the GI lumen occurs when intracellular levels of the second messenger, cyclic adenosine monophosphate (cAMP), increase within enterocytes. Increased intracellular cAMP concentration promotes chloride secretion.3 Thus, diarrhea caused by excessive secretion of fluids is called secretory diarrhea. Secretory diarrhea characteristically contains large amounts of fluid and is described as watery. Secretory diarrhea is observed in certain infectious diseases such as cholera or infections with rotavirus. Secretory diarrhea also can be observed in endocrine disturbances associated with carcinoid syndrome or vasoactive intestinal peptide (VIP)-secreting tumors.
4 Diarrhea due to increased osmotic load. Many substances that are taken orally and are not fully absorbed can exert a significant osmotic force, overwhelming the physiologic absorptive capacity of the GI tract. A significant number of patients with diarrhea in the ICU fall into this category.